1. Field of Art
This invention relates to caps or closures for containers and in particular to a linerless plastic closure which is adapted to seal containers having internal pressure therein.
2. Brief Description of the Prior Art
Closures for liquid-carrying containers, particularly those closures for application on carbonated beverage bottles, have been predominately metal with a resilient liner incorporated therein to properly effect a seal. The necessity of providing a liner has added to the cost, and there is a need and desire for a one-piece closure that will function as an effective seal after engagement with the bottle.
As desirable as the one-piece plastic closure may be, there are a number of problems associated with its use. First is the problem of maintaining a seal over an extended period of time under various conditions of packing, storage and handling. Plastic materials have an inherent tendency to cold flow or creep under stress; thus, once the closure is firmly engaged on the container, whether by threads or some other means, various parts of the closure are under stress because of forces required to effect a seal. This is particularly true when the container is used to package carbonated beverages, and internal pressure acts outwardly on the closure. A plastic material's tendency to creep is further affected by elevated temperatures. The problem created by creep is to cause a loss of seal, and, as a result, a possibility of leakage or spoilage of the contents.
In order to achieve an effective seal with a one-piece closure, various means have been employed. Plunkett U.S. Pat. No. 3,055,526, Healy U.S. Pat. No. 3,160,303, Gibson U.S. Pat. No. 3,232,470 and Braun U.S. Pat. No. 3,255,908, to cite a few, have relied upon the sealing action to take place on the uppermost face of the container opening. Others, such as Miller U.S. Pat. No. 3,074,579, Fox U.S. Pat. No. 3,142,402, Grussen U.S. Pat. No. 3,462,035, Landen U.S. Pat. No. 3,741,424 and Salminen U.S. Pat. No. 3,209,934 depend at least in part for a seal on an annular wall descending from an upper end wall on the cap, and said annular wall impinging against the inside surface of the container neck. The annular wall in a closure of this type functions as a plug, and the effectiveness of the seal relies upon an interference fit between the plug and the inside of the container neck.
A problem with the performance of either of the two aforesaid types of closures relates to manufacturing tolerances on the container. The manufacturing tolerances are broad; the inside diameter of the neck can vary to such an extent that there may be too much interference between the plug and the container opening or there may be so little interference that an effective seal cannot be made; likewise, the top face of the rim on the neck of the container and the inside of the neck may be rough or uneven and thus have an adverse effect on the seal.
Another inherent problem with the use of closures for pressurized containers, and especially those closures utilizing plug seals, is that of "blow-off" or, as it is sometimes called, "closure missiling". On a threaded closure, the cap must be unscrewed to the point where pressure is released while sufficient thread engagement remains to keep the closure from being propelled from the bottle. There is no control over the method used to unscrew the closure in that the consumer effects such unscrewing. The method varies from repeated twisting actions in the range of 90.degree. rotation each to 360.degree. rotation in one twist. Any combination of these is possible. Release of pressure therefore should be as near instantaneous as possible to eliminate problems associated with different opening techniques. U.S. Pat. No. 4,007,851 discloses a solution to the "closure missiling" problem as it pertains to rolled-on metal closures. U.S. Pat. No. 2,990,079 shows a one-piece threaded plastic closure that employs a gas-venting means, and U.S. Pat. No. 3,994,104 discloses a threaded wine bottle stopper comprising a one-piece threaded cap and plug having a gas-venting means.
Accordingly, a linerless plastic closure is desired that cooperates with bottles made by different manufacturers which will provide a reliable seal on glass or plastic containers for pressurized liquids and will minimize the chance of accidental "blow-off" during removal of the closure from its container.
Although the majority of the experimental and developmental work on the present invention was directed toward using the closure with a plastic container, it is believed that the closure is suitable for glass containers as well.